1. Field of the Invention
This invention relates to a method of diagnosing image processors in which image data of an image is compressed and then stored in memory and the compressed image data is read from the memory and then expanded to obtain the original image data for the output of the image.
2. Discussion of the Related Art
Digital copying machines and facsimile machines read the image of a document by an image input unit to obtain image signals and these image signals are digitized to produce image data.
For example, in digital copying machines image signals from an image input unit are generally either processed almost in real time and directly applied to an image output unit or stored in memory in digitized form on a page basis, properly processed, and applied to the image output unit. To increase the copying efficiency, the digital copying machines are also used in combination with an automatic document handler (ADF) or a recirculating automatic document handler (RDH).
An example is a digital copying machine equipped with an ADF which prepares n copies of a document consisting of m pages in sorted form. Copying with an ordinary ADF not capable of recirculating documents requires that n copies be produced successively for each page of the document and that the produced copies be discharged sequentially into n bins using a sorter, and this operation must be repeated for m times to have a set of m-paged copies sorted, one copy in each bin. Copying with an RDH, on the other, allows the required number of copies to be produced in sorted form without using a sorter. That is, m pages of the document are copied sequentially once and the processed copies of m pages are discharged into a discharge tray, and thereafter, the document is recirculated as many times as the required number of copies. However, in the RDH, the document must go through belts and rollers so many times that the risk of a mechanical problem, such as a jamming of the machine, is much increased.
To overcome this shortcoming, it has been proposed that all the image data of the document be stored once in a large-capacity memory and that the stored data be read in proper sequence to be output onto a recording sheet.
For example, all the images in m pages of a document are read by the image input unit to obtain their image signals. The obtained image signals are then converted into corresponding digital signals and stored in a hard disk unit. If the stored digital signals are repeatedly read and output from the hard disk unit in the order of first, second, third, to mth page, first, second, third, to mth page, and so on, a required number of copies can be prepared in sorted form without using a mechanical sorter nor causing the document to be read more than once. That is, electronic recirculating document handling can be achieved.
Further, the image output unit of the copying machine may also be used as a printer for another image data source, e.g., a work station, if it is so arranged that a job can be accepted from another image data source through a communication line and applied to the image output unit during a period in which a job is being read from the image input unit and stored in the storing unit. And upon end of the job from the work station, the stored image data of the document can be read from memory unit and applied to the image output unit to produce copies.
Accordingly, shared use with a workstation of the image output unit of the copying machine contributes to streamlining units of similar function and also eliminating wasteful wait times, thereby utilizing the machine fully. The term "job" herein used is intended to mean a block of image data which is subjected to the same processing.
However, the image data read from the document can be so voluminous that even the use of a large-capacity memory such as a hard disk cannot accommodate all the data. Thus, a technique of storing image data by first compressing it is employed to reduce its volume. To obtain the original data, the codified, or compressed, image data must be read and expanded by an expander. Accordingly, this technique involves both compressor and expander units. The compressor and the expander are usually made up of expensive large scale integrated circuits (LSIs), and the chips thereof are mounted on printed circuit boards.
The above image processor with the compressing and expanding functions will produce greatly distorted images if its compressor or expander unit fails. In fact, distortion of the image may suggest trouble with either the compressor or the expander or both. Thus, whenever the output image is distorted or abnormal, both the compressor and the expander unit must be inspected to find the problem.
In the related art of image processors, the inspection comprises the steps of compressing image data having a predetermined pattern by the compressor, recovering the compressed image data by the expander, and comparing the recovered image data with the original image data. If the compression and expansion are performed normally, both image data under comparison will coincide with each other.
However, such self-diagnosis informs the user only of the presence of an abnormality when there exists a disagreement between the recovered and original image data but not of which unit is causing the abnormality. Thus, the user must remove both the compressor and the expander chips taken from the respective printed circuit boards and replace them with good LSIs or perhaps exchange entire printed circuit boards. This method is disadvantageous in that it not only entails high cost but also does not identify the exact cause of the trouble, thereby making it difficult to take effective measures to prevent future problems. In the case of a system of nonreversible compression in which the recovered data does not always coincide with the original image data even under normal operation, such comparison is of no use in verifying the operating condition.